Power supplies are generally used for the current-specific operation of electrical loads; in particular, a time-dependent current path through a load should be adjustable. Rectifiers offer a reliable and proven approach for supplying large currents. However, they deliver a ripple output voltage and thus a ripple output current.
A very high accuracy of solenoid current is required to supply accelerator magnets in accelerator systems. For this reason, conventional rectifier approaches for supplying power to accelerator magnets provide for LC filters to be used (see, for example, “New Principle for Power Supplies for Synchrotron Magnets Without Tracking Errors” by R. Fink and G. Breitenberger et al., 2nd European Accelerator Conference, Nice, Jun. 12-16, 1990, pp. 1188-1190, FIG. 1 therein). These have poor dynamic properties since, in terms of automatic control engineering, a second order system is created by the filter and the load magnet.
Synchrotron accelerators require ramp-controlled power supplies. The poor dynamic performance and the unavoidable lag errors caused by the requisite PI controller during the current ramps makes the above described, classic rectifier approaches unsuited for these applications.
“New Principle for Power Supplies for Synchrotron Magnets Without Tracking Errors” by R. Fink and G. Breitenberger et al., 2nd European Accelerator Conference, Nice, Jun. 12-16, 1990, pp. 1188-1190 discusses a power supply that is able to make do without a passive LC filter at the output of the rectifier. The power supply is composed of a 12-pulse rectifier, SCR (=silicon controlled rectifier), which handles the bulk of the load current, and a load-parallel active filter, referred to as the parallel injection, PE, which only handles a small portion of the load current, but provides for the accuracy and stability of the load current. However, the method described requires a substantial technical outlay to minimize the losses in the linearly controlled transistor banks. To this end, a complex control is also necessary.
As discussed in “Power Converters of the Main Dipole and Quadropole Magnet Strings of the Antiproton Decelerator at CERN” by F. Volker et al., CERN/PS 2000-016 (PO), 7th European Particle, with respect to its steady-state and dynamic behavior, a phase-controlled thyristor rectifier can be improved for high-precision and rapid-response applications through the use of a parallel, pulse-width controlled active filter. Again, the rectifier handles the bulk of the load current, while the active filter merely handles the harmonic cancellation and current-error compensation, and is only used for a portion of the load current under transient conditions. This leads to a low power rating of the active filter. In this approach, the clock filter at the output of the active filter makes it additionally necessary to have a passive LC filter at the output of the rectifier in order to observe the required accuracy, thereby entailing the above described disadvantages.